This invention generally relates to a system for coupling machine tools, and is specifically concerned with a system for detachably coupling machine tools to the toolholders of a modular tooling system by means of a small package having a high holding force that provides accurate and rigid tool couplings in all six degrees of freedom at both low and high rotational speeds.
Coupling systems for interconnecting machine tools are well known in the prior art. Such coupling systems include a hollow, frustro-conical male component that forms part of the tool which mates with a frustro-conical opening in a female component. The female component is typically part of a spindle for rotating the tool. The taper of both the frustro-conical components often has a slope of about 1 to 10 with respect to the longitudinal axis of the tool. Such a slope provides a rigid, on-center interference coupling when the components are pulled together by means of a clamping mechanism disposed in the interior of the female opening.
There are presently a variety of mechanisms for clamping together the frustro-conical male and female components of prior art coupling systems. In some of these mechanisms, the female component on the toolholder includes radially movable locking balls for engaging complementarily-shaped socket openings in the walls of the male component. When moved radially outwardly, the locking balls function to secure and pull in the frustro-conical tool shank into the frustro-conical opening in the toolholder. An axially slidable bolt having cam surfaces radially forces the locking balls outwardly into the socket openings. In other types of mechanisms, the female opening includes a radially expandable locking plunger which is extendable into the hollow interior of the frustro-conical male component. The locking plunger may include two or more radially movable fingers that engage openings in the wall of the frustro-conically shaped male component in order to forcefully wedge the male component of the tool into the female component of the toolholder.
While both of these general types of prior art coupling systems have shown themselves to be effective for their intended purpose, systems fabricated by different manufacturers are unfortunately not interchangeable with one another. Thus the end user of a tooling system has, up to recently, been forced to choose between one particular proprietary type of tooling and coupling system or another. To remedy this problem, the German government in 1987 standardized the dimensions of the envelope that such coupling systems were to have in a proclamation entitled "DIN 69890". However, this proclamation did not standardize the aspect ratio or type of coupling mechanism that was to clamp together the frustro-conical male and female coupling components. Specifications for a coupling system sufficiently standardized to permit interchangeability did not occur in Germany until the issuance of DIN 69893 in 1993 which sets forth the dimensions of the frustro-conical male component and female taper area that would secure the components together. This proclamation also specifies that the male component is to have an annular shoulder circumscribing its interior that defines a follower surface. By implication, the female component is to have a member with a cam surface that engages the male follower surface to lock the two components together. The standardized coupling system specified in DIN 69893 is already being manufactured by several German-based tooling companies, whose tooling systems are being sold to several of the major German automotive manufacturers. The growing implementation of DIN 69893 in Germany and elsewhere is likely to result in the adoption of these same specifications internationally.
DIN 69893 generally sets forth the dimensions and type of follower surfaces in the male component that are to be used to couple the components together. However, it does not specify the form that any cam members in the female component should take, or what drive mechanism is to be used to move these cam members into engagement with the follower surface within the male component, as different cam members and drive mechanisms can be used without impairing the interchangeability of coupling systems fabricated by different manufacturers. There presently exists a number of such cam designs and drive mechanisms. Unfortunately, there are a number of shortcomings associated with each.
For example, almost all prior art drive mechanisms employ an axially movable draw bar that expands the cam members by a camming action. While such draw bars may be used in applications where there are few if any axial space constraints (such as when the coupling system is used to connect a tool to the spindle of a machining center), they are difficult if not impossible to use in modular tooling systems where the overall size of the coupling envelope may not exceed a certain specified length. Still other shortcomings associated with draw bar type mechanisms is the fact that substantially all of the mechanical advantage used to generate the coupling force is derived from an axially oriented screw thread accessible only on the end of the tool, rather than on its side. The axial orientation of such screw threads makes access difficult in modular tooling systems where the tools are closely spaced, and impedes the operator's ability to change tools quickly. Additionally, the primary reliance upon a screw thread for the generation of mechanical advantage can lead to excessive wear between the screw threads and the threaded bore which receives it, which in turn can lead to inconsistent coupling forces over time.
Since the tensile force generated by the clamping mechanism causes the frustro-conical male and female coupling components which mate with an interference fit to tightly wedge together, some means must be provided for positively pulling or "bumping" these components apart when a change in tools is desired. To this end, many prior art plunger-type coupling systems include some sort of bumping mechanism. But, many of these mechanisms rely upon a spring to provide the necessary impulse to "bump" the male and female components apart. The use of springs not only complicates the coupling mechanism, but can result in an unreliable bumping action. While some of the aforementioned deficiencies of plunger-type clamping mechanisms could be overcome by the use of a locking ball mechanism, the use of locking balls requires the provision of holes through the tapered walls of the male component of the tool. Such holes are not allowed in the specification of DIN 69893.
Clearly, there is a need for a drive mechanism for radially expanding the cam members needed in DIN 69893 coupling systems which is sufficiently compact in the axial direction to be easily used in modular tooling systems. Ideally, the drive mechanism would afford an easily accessible radially-oriented actuator for the machine operator to facilitate quick tooling changes, and should be capable of applying large amounts of pull-back force between the frustro-conical male and female components with a high degree of mechanical advantage. Preferably, the drive mechanism should avoid the concentration of excessive pressures in any particular portion of its components which could result in excessive wear, shortened tool life, and inaccurate coupling forces between the male and female coupling members. Finally, the drive mechanism should provide a positive and reliable "bumping" action between the male and female components in order to effect quick tooling changes, and should be relatively easy and inexpensive to manufacture, and easy to assemble and disassemble and maintain.